With a biogas generation system, large volumes of manure are digested under low-oxygen conditions to produce biogas that is subsequently combusted to destroy methane and produce heat or electricity. The waste sludge is normally returned to the land as fertiliser, either as slurry or pellets.

Summary

The destruction of methane will increase farm viability by attracting Australian Carbon Credit Units (ACCUs) under the Emissions Reduction Fund (ERF). The ERF has four approved methodologies for the destruction of methane by pork and dairy farmers, which include covered anaerobic ponds and engineered bio-digesters.

These methods set the upper limit of the abatements that may be claimed by determining the baseline emissions that would have occurred with uncovered waste ponds.

The simplest method is to capture the gas and combust it in a flare. More complex systems offset energy costs either by combusting the gas to produce heat or by combusting it in a generator for the cogeneration of heat and electricity. If the energy generated exceeds farm requirements, the excess may be exported to the grid.

Biogas generating facilities are usually added to existing manure storage ponds. The process of using biogas is as follows:

Waste ponds are covered to prevent methane escaping into the atmosphere. The cover consists of an impermeable membrane stretched across the pond. It is sealed at the edges in anchor trenches with gas-collecting pipes located underneath the cover. A mechanism must be installed to drain rainwater so it does not pool excessively and collapse the cover.

Biogas is collected and piped away from the pond.

Biogas is combusted, converting methane to carbon dioxide and water. The remaining waste solids are a concentrated form of nutrients that can be used as fertiliser.

Benefits

Commercial

Destroying methane via a biogas system attracts ACCUs through the ERF.

Intensive livestock farmers can potentially offset the cost of energy bills with on-farm generation and may even generate income through selling electricity back to the grid (depending on size and the availability of infrastructure).

Co-benefits

Covering manure ponds reduces odours.

Sludge waste may be pelletised and sold as a nutrient-rich fertiliser. For example, specialist equipment company Satake Australia has a facility in South Australia that is capable of producing 7.5 tonnes of finished product per hour across a range of fertilisers.

Opportunities

Methane destruction is on the positive list for the ERF; in other words, the practice is eligible for carbon credits.

Biogas generation is suitable for integration into current farming systems. After some infrastructure expenditure, a system to destroy methane can reduce running costs and control odour, as well as provide a potential source of income.

In WA, about 40 piggeries and 30 dairies are large enough to make biogas generation profitable.

Risks

Price volatility for ACCUs.

Underestimation of greenhouse gas emissions from waste ponds.

Although technology associated with anaerobic ponds and biogas systems has been developed over the past 40 years, the systems are not fail safe: